Multipurpose transducer housing plug with acoustical vent



June 2, 1970 M. DE NARDI ETAL 7 3,515,821

, MULTIPURPOSE TRANSDUCER HOUSING PLUG WITH ACOUSTICAL VENT Filed Nov. 17, 196e 2 sheets-sheet 1- E5- Z /7 v ...fi-5'. 2-

June 2, 19,70 3,515,821

MULTIPURPOSE TRANSDUCER HOUSING PLUG WITH ACOUSTICALVENT I Filed Nov. 17, 196e lM. DE NARDI ETAL 2 Sheets-Sheet 2 Ez-EIA- r ww www. mw W f ,v i f4 ma 67 L HU, m e MW M United States Patent 3,515,821 MULTIPURPSE TRANSDUCER HOUSING PLUG WITH ACOUSTICAL VENT Mario De Nardi, Yorktown Heights, and William F.

Knauert, Yonkers, N.Y., assignors to Sonotone Corporation, Elmsford, N .Y., a corporation of New York Filed Nov. 17, 1966, Ser. N o. 595,136 Int. Cl. H04r 1 06, 1/28 US, Cl. 179-179 3 Claims ABSTRACT F THE DISCLOSURE An electro-acoustic transducer assembly including a novel multipurpose plug which is so located as to provide the maximum acoustic cavity for a given housing, which at the same time acoustically seals the transducer assembly housing, is designed to provide cable bend relief and strain relief, and which includes a vent means for the above-mentioned cavity.

Electro-acoustic transducer assemblies, or transducers, such as microphones and earphones, usually employ a vibratable member, e.g., a diaphragm, which is mounted Within the transducer housing and which is mechanically vibrated by sound waves striking it or is electrically vibrated to create sound. In the design of commercial transducers, there is a problem of providing a suicient acoustically sealed cavity volume within the housing behind the diaphragm to obtain optimum performance without unduly enlarging the housing. The plug is located to perform the sealing function.

Electro-acoustic transducers contain a sound sensing or producing means, e.g. the diaphragm noted above, which comprises part of the transducer. This means is typically connected to an electric signal receiving, transmitting or amplification mechanism by an externally extending cable which passes through an aperture in the transducer housing.

During normal usage of a transducer, as it is moved about by an operator, the cable is subjected to considerable flexing near the point along its length where it enters the transducer housing. To prevent the cable from breaking near this point due to repeated flexing, a means to provide .bend relief for the cable is usually provided. Such means might be comprised of a resilient sleeve positioned around the flexing portion of the cable to distribute the flexing over a greater region of the cable so as to prevent the occurrence of an abrupt or sharp bend in the cable where it enters the housing.

Additionally, during normal usage of the transducer, the cable is subjected to pulling and pushing which might loosen the electrical connections 'between the cable and the transducing assemlbly or which might pull the cable entirely out of the housing, unless some means is provided to counteract the effect of these stresses on the cable. Accordingly, means to provide strain relief for the cable is employed to minimize the effect of these stresses.

It has been known in the art to provide a controlled venting means which connects the cavity of the transducer housing either to another housing cavity or to the outside of the transducer. Such controlled venting can have for its purpose pressure relief only (when needed) without significantly affecting the response or it can change the low frequency response by attenuating the low-low frequencies and building up the mid-low frequencies by the resonant effect of tuning the venting system so as to give a desired response often required when speech applications are paramount. See, e.g., co-pending application Ser. No. 523,618, led b-y William Knauert, one of the inventors herein, and by Martin Molloy, and as- 3,515,821` Patented June 2, 1970 AICC signed to the assignee of the instant invention now Pat. No. 3,439,129. If it is desired to have controlled venting of the cavity of the transducer housing, the plug of the instant invention is adaptable to receive venting means.

The prior art shows separate structures tol perform each of the functions of bend relief, acoustic sealing, strain relief and venting. It is desirable to provide a simple and economical means for performing these functions in the smallest possible transducer housing to give maximum latitude for appearance designing. Accordingly, the present invention provides a multipurpose transducer plug which is simple and economical to manufacture, which is aesthetically pleasing, and which simultaneously performs the functions of bend relief, strain relief, and acoustic sealing, and is adaptable for performing the venting function.

While the plug of the instant invention can be used in conjunction with any electro-acoustic transducer, for illustrative purposes the description herein Will be concerned with microphones. This is not intented to limit the scope of this invention.

Usually, the plug of the instant invention is used in connection with a microphone comprised of a hollow, thin, generally cylindrical housing ha-ving a microphone cartridge within it near one end. The plug of the instant invention can be used with microphone housings having other shapes than that just described, so long as the functions of sealing, .bend relief, and strain relief must be performed and also Where it is determined that venting is required. The cartridge contains a transducer means comprising a diaphragm Vibratable by sound waves and a mechano-electric conversion means to transduce the mechanical vibration into electrical impulses. One end of a cable is connected with the transducing means and passes from within to without the microphone housing through an aperture in the housing. The multipurpose plug of the instant invention closes the aforesaid aperture in the housing and the microphone ca'ble passes through another aperture through the plug. The plug of the instant invention provides an acoustic seal since it is of resilient material and is dimensioned to tit tightly inside the housing and around the cable. The plug provides strain relief since the aperture through which the cable passes has a smaller cross section than the cross section of the transducer cable, whereby the cable is securely held by the force exerted lby the walls of the aperture through the plug. The plug is comprised of resilient material which enables the broader cable to be passed through the narrower plug aperture. The pulling and pushing stresses on the cable are absorbed by the plug rather than by the connections between the cable and the transducing means.

The plug also surrounds the cable over a significant portion of its length to provide bend relief. As the cable is flexed near the end of the microphone housing out of which the cable extends, the resilient plug spreads the exing over an enlarged region of the cable, whereby sharp bending of the cable near the end of the housing s precluded. To aid in the bend relief, the plug surrounds the cable for a distance outside the microphone housing.

If it is desired to adapt the plug of the present invention to provide controlled venting of the microphone, Venting is accomplished by providing a section for a second aperture which extends through the sealing section of the plug from within the cavity of the microphone housing to a channel communicating With the outside or With of the plug and extends completely through the sealing section. i,

Accordingly, it is a primary object of the present invention to provide a transducer assembly having a multipurpose plug that performs the functions of sealing, bend relief, strain relief and which is adaptable for venting of the transducer housing.

It is a further object of the present invention to provide a transducer assembly having such a multipurpose plug which can be simply and economically manufactured and which has a minimum of parts.

It is another object of the present invention to provide a multipurpose transducer assembly plug that can be used in conjunction with a transducer in accordance with the preceding objects.

These and other objects of the present invention will become apparent after the following description is read in conjunction with the accompanying drawings, in which:

FIG. l is a cross sectional view in elevation of `a microphone adapted with the multipurpose plug of the instant invention.

FIG. 1A is a simplified schematic drawing of the electric circuitry of the microphone of FIG. 1.

FIG. 2 is a view of the microphone of FIG. 1 in the direction 2-2 showing the microphone housing partially broken away.

FIG. 3 is a cross sectional View in elevation of the multipurpose plug of the instant invention.

FIG. 4 is a plan view of the plug of FIG. 3.

FIGS. 3A and 4A show the plug of lFIGS. 3 and 4 adapted to perform the venting function.

FIG. 5 is a view in the direction 5--5 of the plug of FIG. 3.

Referring to the figures, FIG. 1 shows a microphone, which is an electro-acoustic transducer assembly. The microphone has a housing 11 which is hollow, cylindrical and generally circular in horizontal cross section. The cylindrical housing 11 defines a cavity 12 within itself. The housing 11 is open both at its front end 13 and its back end 14. The housing structure is bent at 15, forming thereby an annular ange 16 which surrounds the opening 14a in the housing end 14.

The open forward end 13 of the microphone housing 11 is covered by a sound Wave permeable dress grille 17. Disposed beneath the dress grille is a wind screen 48 which protects the hereinbelow described vibrating diaphragm member 23 from damage causedby the pressure exerted by wind or by breath being exhaled by the microphone user.

A sound sensing and transducing cartridge 20 is disposed within the housing cavity 12 and faces the forward end 13 of the microphone. The mounting ring 21 holds in position a support 22 for the cartridge 20 and acoustically seals end 13. Sound waves entering the forward end 13 of the microphone cause vibration of a vibratable acoustic member 23, which may be a diaphragm, and which may be comprised of a thin vibratable sheet of metal or plastic. The vibration of the diaphragm 23 is converted into electrical impulses by any one of a number of transducer means which are well known in the art. One such means, a mechano-electric -transducer means, will be described herein for illustrative purposes.

The transducer means shown in FIG. lcomprises a yoke 25 for supporting other elements of the transducer means. The yoke 25 is attached to the support member 22. Yoke 25 can be comprised of a single strip of material, e.g., metal,which is bent into a U shape, or of a cup shaped element having portions cut out of its side walls, or might be otherwise comprised, so long as `it serves as a suitable support for the hereinbelow described magnet 26. As can be seen in FIG. 2, the width of the yoke 25 is less than the diameter of the cavity 12 within the housing 11 whereby the diaphragm 23 is exposed to the air column behind the diaphragm within the cavity Y 12, The air column is vibrated by the diaphragm and atfectsthe vibration of the diaphragm, e.g., if the column is short, low frequency sounds are attenuated. Furthermore, as can be seen in FIG. 1, the yoke 25 has cut out sides, thereby aiding theexposure of diaphragm23 to the air column 'Within cavity 12.

Permanent magnet 26 is mounted on yoke 25. Magnet 26 has pole piece 27. p

VA coil28 of 4wire surrounds the pole piece 27 and is spaced away therefrom. The coil 28 is secured beneath the diaphragm 23, whereby vibration of the diaphragm 23 vibrates the coil 28 through the magnetic field around g the pole piece 27 of the permanent magnet 26.

Such vibration induces a voltage in the coil 28 which is taken from'the coil 28 by the coil terminal leads 29 and 30. From the foregoing, it is apparent how the sound wave caused vibration of the diaphragm 23 is transduced into electrical impulses. Referring to FIGS. 1, 1A and 2, panelboard 31 iS positioned within cavity 12, c g. by being wedged against the interior surfaces of housing 11. The panelboard has terminals 29a, 30a, 37a and 38a. Terminals 30a and 38a are electrically grounded to the microphone housing by element 32.

Leads 29 and 30 are connected to terminals 29a and 30a, respectively, on panelboard 31.

Transformer 36, which is mounted within housing 11, is connected by leads 34 and 35 to the terminals 29a and 30a on the panelboard 31 to which the leads 29 and 30 are connected. The transducer means generated electrical impulses are stepped-up in the transformer 36 and are then passed through leads 37 and 38 back to terminals 37a and 38a on panelboard 31 and from there into leads 39 and 40. All of the foregoing elements activated by diaphragm 23 comprise the transducer means.

Lead 39 is the center conductor and lead 40 is the shield of coaxial cable 50. Cable 50 is surrounded by a sheath of flexible protective insulation material. Cable 50 exits from housing 11 through aperture 14a in end 14 thereof and terminates, for example, in a connecting plug 51. The connecting plug may be connected to an audio amplifier (not shown) or other electrical impulse receiver. Cable 50 and plug 51 comprise the cable assembly.

The cartridge 20 acoustically seals end 13 of the housing. Opening 14a in end 14 of the housing must also be acoustically sealed and the multipurpose plug 60 of the instant invention performs this function.

During normal usage of the microphone of FIG. 1, as the microphone is moved about, the exible cable 50 will be subjected to repeated flexing near the point of entry of the cable into the housing 11. The cable may be flexed rather severely and may be bent at very sharp angles as a result of normal movement of the microphone. Repeated ilexing and bending of the cable near the point of entry into the microphone housing mayeventually weaken the cable and/or the lead wires running through it and might cause breakage thereof. A means to provide bend relief for the cable in the vicinity of its point of entry into the microphone housing is, therefore, required. The multipurpose plug 60 of the instant invention performs this function.

As was previously noted, the leads 39 and 40 which pass into the cable 50 are electrically connected to terminals on the panelboard 3.1. During normal usage of the microphone, the cable 50 is pulled and pushed, whereby the fixed terminal connections of the leads 39 and 40 may eventually be weakend or broken off. The cable 50 itself can have its sheath constructed to be able to withstand the repeated pulling and pushing stresses of normal usage. However, the electric terminal connections cannot be readily made strong enough to withstand `these stresses. Accordingly, a means for providing strain relief for the cable 5t) is needed, whereby the stresses on the cable can be absorbed elsewhere than by the terminals to which the leads 39 and 40 are connected. The multipurpose plug 60 of the instant invention performs this function.

For aesthetic reasons, and for ease of handling, it has been found desirable to design microphone housings, such as housing 11, to be small in size. As a result, the cavity 12 within the housing is also small in size. The diaphragm 23 is vibrated by the sound waves striking it. However, its vibration is affected by the length of the column of air within the cavity 12 behind the diaphragm. If the cavity is very small, it becomes acoustically stiff and the vibrations of the diaphragm are attenuated and the sensitivity of the microphone is impaired. To counteract this drawback, without increasing the size of the microphone housing, the maximum volume of acoustical cavity behind the diaphragm is obtained by locating the sealing plug at the very end of the housing. Since the cavity 12 need not also contain separate bend relief and strain relief structures, the plug 60 herein permits the volume of the cavity 12 to be larger than was previously possible.

If it is felt necessary to provide a venting means for the cavity 12 (e.g., to suitably modify the low frequency response), the multipurpose plug 60 of the instant invention is adaptable for performing this function.

The acoustic sealing, bend relief, strain relief and venting can be combined in one simply constructed, economical and easy to mount multipurpose plug 60, the details of which are shown in FIGS. 3-5. The plug 60 has a longitudinal axis 60a and a circular horizontal cross section. An aperture 61 extends through the plug 60 parallel to its longitudinal axis 60a. As can be seen in FIG. l, the cable 50 is passed through the aperture 61, and the portion 52 of the cable 50 remains within the aperture 61.

Referring to FIG. l, the plug 60 acoustically seals the end 14 of housing 11 because the cross section of its sealing portion 63 is shaped to match the cross section of lower section 18 of housing 11, whereby the outer surface of portion 63 of plug 60 is acoustically sealed against the internal surface of housing section 18. To enhance the acoustic seal, the cross section of portion 63 can be greater than that of section 18 of housing 1.1. This interference lit between the portion 63 of the plug 60 and housing section 18 serves to acoustically seal the cavity 12. Cable 50 is also securely held by the walls of plug aperture 61 completing the acoustic sealing of cavity 12. The interference t between plug 60 and housing section 18 is effective in compressing the plug material so that it adds substantially to the force exerted on the cable 50, thereby effecting a significant improvement in the hereinbelow described strain relief.-

In order for the plug 60 to provide strain relief for the cable 50, thereby to protect the leads 39 and 40 from the stresses of normal pulling and pushing of the cable, a means for providing strain relief is provided, whereby the cable 50 is restrained from moving lengthwise through the aperture 61. To accomplish this, the cross section of the aperture 61 is made smaller than the cross section of the cable 50, whereby the portion 52 of the cable 50 is frictionally engaged by the resilient wall of the aperture 6.1 and the stresses due to pushing and pulling of the cable S0 are absorbed by the plug 60, rather than by the leads 39 and 40.

The plug 60 might be comprised of a resilient material, e.g., processed rubber or suitable elastomer, which would ease the insertion of the wider cross section cable through the smaller cross section aperture 61. If rubber is employed, the plug will establish firm frictional engagement with the cable S0 to ensure strain relief. The resiliency of the material of which cable 50 is comprised would permit its insertion through aperture 61.

As an alternative to, or in combination with, the features just described, if the cross section of plug portion 63 is greater than that of housing section 18 to enhance the acoustic seal, when plug 60 is assembled in housing 11, the pressure on the plug material at its portion 63 will cause the walls of aperture 61 to tighten around the cable portion 52 effecting a significant improvement in strain relief.

The plug 60 has a narrow outside diameter portion 62 which, as can'y be seen in FIGS. l and 2, is normally located outside the end 14 of the microphone housing 11. As was noted above, the entire plug 60 might be comprised of a resilient material. In any event, the portion 62 of the plug 60 should be comprised of a resilient material. The portion 62 has a suiciently small outside diameter so that it is able to ex while securely holding the cable. When during normal usage of the microphone of FIG. l, the cable 50 is caused to flex near the end 14 of the housing, such exing causes bending of the portion 62 of the plug. The resilient plug is not as easily sharply bent as the cable 50 and the portion 62 prevents the cable 50 from being sharply bent near the end 14 of the housing 11. The radius of curvature of the bending of the cable 50 in the vicinity of end 14 of housing 11 is thus increased. Thus, the resilient portion 62 of the plug 60 provides bend relief.

On some occasions it may be necessary to provide controlled venting of cavity 12. Plug 60 is adaptable for providing venting because of its construction. The sealing portion 63 of the plug has a shelf 64 Which is indented from the top of the plug 60. The plug 60 also has an annular groove 65 extending around it for mounting purposes, as will be described below. The groove 65 is in planes substantially perpendicular to the axis 60a of the plug 60. There is provision for an aperture 66 substantially parallel to the plug axis 60a, extending through the plug 60 from the shelf 64 to the groove 65.

Plug 60 is also provided with a channel 67 the axis of which is substantially parallel to the axis 60a of aperture 61 and the projection of which is substantially centered within the area of the shelf 64. The channel 67 extends from a point somewhat above the top edge of groove 65 to a point substantially below the bottom edge of groove 65 on tapered plug portion 71. The innermost surface 68 of channel 67 extends deeper in towards the axis of the plug than the innermost groove surface 65a.

When it is desired to alter the low frequency response of the microphone by acoustic venting, the plug 60` can be adapted for venting. The adapt plug 60 to perform the venting function a hollow cylindrical venting tube 70 (FIG. l) is provided comprised of a nondeformable material, e.g. metal. The venting tube 70l has a predetermined length and an aperture 66 of predetermined cross section to obtain desired optimum acoustical properties for each type of microphone.

The rigid tube 70 of predetermined length and cross section is positioned with its axis substantially parallel to axis 60a of aperture 61. The outer wall surface of the tube 70` may be placed in contact with the innermost surface 68 of channel 67because surface 68 can serve as a guide for insertion of tube 70. Tube 70 is then pushed up and made to pierce through sealing section 63 under shelf 64 so that tube end 70a is flush with or extends slightly below end surface 69 of channel 67 and end 70b is within the projection of channel 67. The length of tube 70` is such that end 70b extends above shelf 64. When the plug 60 is positioned in the end 14 of the housing 11 a portion of the channel 67 will be outside the end of the housing 11 and an air path is provided between the cavity 12 and the outside of the microphone by the combination of the aperture 66 in tube 70 and the channel 67. In order to prevent the annular flange 16 of the housing from interfering with the free air passage between aperture 66 and channel 67 when the plug 60 is mounted as hereinafter described, the channel 67 extends deeper into the plug 60 than the groove 65.

l It is to be understood that although one of the embodi- 'ments shown in the figures shows a venting aperture66 which connects the cavity 12 to the outside of the micro# phone, it is within the contemplation of the invention to have a multipurpose plug with a venting aperture that connects the `cavity of a microphone with another enclosed microphone cavity. l In assembling the microphone the stripped end of cable 50 is fed vthrough aperture 14a, cavity 12 and aperture 13. `Suitable means well known in the art are used to stretch aperture 61 of plug 60` to permit easy insertion of the stripped end of cable S through aperture 61. Plug 460 is positioned at a predetermined distance from the stripped end of cable 50. All components including panelboard 31, cartridge 21, and transformer 36 are brought together and electrical connections made as required, preferably outside the housing. The cable 50Y is then pulled back through aperture 14a '(making sure that the transformer 36 is located below panelboard 31) until end 62 of plug 60 appears through aperture 14a. The plug 60 has a tapered portion 71 to permit ease of assembly in the housing 11. End 62 of plug 60 is pulled through aperture 14a of the housing 11 until the annular ange 16 of the housing slips into the groove 65 of the plug 60. The plug 60 is now mounted and the remainder of the microphone can be assembled.

By employing the plug 60 in a transducer such as the microphone shown in FIG, 1, acoustical sealing, strain relief, bend relief and venting, when desired, of the transducer can be obtained by employing a simply constructed economical multipurpose plug inserted into the transducer housing.

Although there has been described a preferred embodiment of this novel invention, many variations and modifications will now be apparent to those skilled in the art. Therefore, this invention is to be limited, not by tthe specific disclosure herein, but only bythe appending claims.

The embodiments of the invention in which an exclusive privilege or property is claimed are dened as follows:

1. In an electro-acoustic transducer housing assembly having a closed end and an open end and defining a cavity within itself, transducer means within said housing assembly for providing a mechano-electric conversion, and an elongated tlexible cable connected to said transducer means and exiting from said housing assembly through said open end, the improvement comprising:

a plug member; l l y said plug member being positioned within said open end and having a rst aperture therethrough passing 8 fromwithin 'to without said cavity and through'which said flexible cable connects to said transducer means; said vplug member additionallyY having 4a iirst portion of cross-sectional dimension within said cavity at least equalto the cross-sectional dimension of the' corresponding portion of said cavity adjacent said lrst por# tion for acoustically sealing said open end;

said plug member additionally having a resilient por tion overlying said aperture external to said open cavity and of a diameter enabling said resilient portion to ex while holding said elongated cable by an amount less than the'flexing of said cable alone in response to a similar bending force to provide bend relief for said cable;

with the cross-sectional dimension of said plug member aperture being less than the cross-sectional dimen` sion of said elongated cable held thereby to cause frictional engagement therebetween to provide a strain relief in the presence of a pushing and pulling of said cabile towards and away from said transducer means; an

wherein there is also included means for controllably venting said housing cavity to provide pressure relief for air trapped within said housing and a moditication of the frequency response characteristics of the electro-acoustic transducer assembly.

2. The plug member of claim 1 wherein said controllable vent means includes a hollow tube of nondeformable material having a predetermined cross-sectional dimension and length for controlling the low frequency response characteristic of said transducer assembly.

3. The plug member of claim 2 wherein said plug member is a unitary element entirely comprised of a resilient material.

References Cited UNITED STATES PATENTS 3,235,674 2/1966 Mirstam 179-179 3,201,530 8/1965 Levy et al. 2,787,675 4/1957 Meshirer et al. 179--179 2,485,278 1071949 Gilman et al 179-121 KATHLEEN H. CLAEEY, Primary Examiner T. W. BROWN, Assistant Examiner U.S. Cl. X.R. 179--186 

